diff options
authorStefan Agner <>2015-06-09 13:38:58 +0200
committerStefan Agner <>2015-06-09 13:48:51 +0200
commit64578b59ff73a1a96f166cf518f58477285117f4 (patch)
parent7ed3ad7562ccdd9dca296b30a556865c772d99e6 (diff)
tty: serial: fsl_lpuart: consider TX FIFO too in tx_empty
Currently the tx_empty callback only considers the Transmit Complete Flag (TC). The reference manual is not quite clear if the TC flag covers the TX FIFO too. Debug prints on real hardware have shown that from time to time the TC flag is asserted (indicating Transmitter idle) while there are still data in the TX FIFO. Hence, in this case the serial core will call the shutdown callback even though there are data remaining in the TX FIFO buffers. Avoid early shutdowns by considering the TX FIFO empty flag too. Also avoid theoretical race conditions between DMA and the driver by checking whether the TX DMA is in progress too.
1 files changed, 12 insertions, 2 deletions
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index b3bc175d70e4..61e59a106858 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -770,8 +770,18 @@ static irqreturn_t lpuart32_int(int irq, void *dev_id)
/* return TIOCSER_TEMT when transmitter is not busy */
static unsigned int lpuart_tx_empty(struct uart_port *port)
- return (readb(port->membase + UARTSR1) & UARTSR1_TC) ?
+ struct lpuart_port *sport = container_of(port,
+ struct lpuart_port, port);
+ unsigned char sr1 = readb(port->membase + UARTSR1);
+ unsigned char sfifo = readb(port->membase + UARTSFIFO);
+ if (sport->dma_tx_in_progress)
+ return 0;
+ if (sr1 & UARTSR1_TC && sfifo & UARTSFIFO_TXEMPT)
+ return TIOCSER_TEMT;
+ return 0;
static unsigned int lpuart32_tx_empty(struct uart_port *port)